How NASA brought the F-1 “moon rocket” engine back to life (2013)
arstechnica.com
arstechnica.com
The fifties were such a crazy time where the USAF would commission wild things which in development were superseded or mooted by other developments, leaving the commissioned object as a cast-off vision of a future that didn't happen. Maybe the high point of this was the XB-70 Valkyrie. [1]
Today is the first day that I put two and two together on North American Aviation making both the XB-70 and the B-1: To take maximum advantage of [compression lift], they redesigned the underside of the aircraft to feature a large triangular intake area far forward of the engines, better positioning the shock in relation to the wing.
To bring things full circle, in 1955 NAA spun off its rocket division, which became Rocketdyne, the maker of the F-1 among other engineering marvels.
0. https://en.wikipedia.org/wiki/Rocketdyne_F-1
1. https://en.wikipedia.org/wiki/North_American_XB-70_Valkyrie
In that environment, it was more reasonable to run parallel development projects, as one didn't want to be caught flat-footed if one approach failed (e.g. SLBM + ICBM + bombers).
It’s slightly wilder. Raptor uses 100,000 hp per engine [1]. That is two F-1 scale turbo pumps per engine, i.e. 66 pumps altogether. All for the dress rehearsal.
Additional facet is that Raptor turbopump is full flow and thus runs at very low (relative to other gas turbine machinery out there like for example F-16 at 1200C+) temps like 500-600C which means that the power can still be almost doubled with the same regular materials they use - steel and Inconel (and this is what we're seeing - about 1.5X power increase from Raptor 1 to Raptor 3 in a span of mere few years while the engine weight is even decreasing a bit)
And the raptors are reusable.
Cool :)
> Additional facet is that Raptor turbopump is full flow and thus runs at very low
You write it further yourself, but rocket turbopump turbines aren't running with cold gas - the hotter the input gas, the more energy can be provided to pumps, so turbine blades have roughly the same requirements as those in F-16. The design on those blades is pretty complex, with materials, processes and substructures like internal cooling channels - all to reach possibly higher temperature to work with.
The useful metric on this front would be thrust density, where Raptor 1 is a bit under twice that of F-1A, Raptor 2 is a little over twice of F-1A, and Raptor 3 should be ~2.5x of F-1A.
And, they do seem to test the heck out of their engines, even with 30 of them on a ship.
Trying to manage that many engines while technically possible with controls of the era (check out the N1) means your control system would be introducing reliability issues instead of adding fault tolerance through redundancy.
[edit] ah. That was the N1 you referred to. Ok. So you're saying it was possible, but it introduced more failure points.. So is that why it failed...
The second was, as mentioned, that the control systems of the time were not that great, so they had issues properly compensating for engine failures, causing them to cascade until too many engines were lost to get to orbit.
Curious what approach you'd propose in their place?
> The second was, as mentioned, that the control systems of the time were not that great
True. The control system was also cutting edge, and evolved together with engines, and also was much better by the 5th flight - which was scrapped - than it was at the 1st one.
The approach used nowadays, make engines that can be fired (at least on the ground) multiple times. As far as I'm aware, all current generation American rockets can be static fired on the ground to verify that they work.
Edit: Although, come to think of it, not necessarily true with vacuum engines, but even then, they can test the turbopumps and have enough sensors to find potential issues before launching (at least once enough experience has been built up on the engine).
Vacuum engines can actually be tested on Earth, some special devices which produce external pressure decrease when the engine is running (like, if you run engine in a tube, the hot gases will push all the air from the tube making a pressure drop).
That was another issue the Soviets had a hard time dealing with.
The whole idea, by the way, of the full-flow combustion is to extract some more energy from the fuel - before sending that fuel to the chamber, and at the temperature which the turbine of the turbopump can tolerate - so that energy could be used for pumps and more pressure could be created in the chamber. More energy than "more conservative" closed-cycle engines.
The pump power is equal to the volume flow (how many cubic meters, or, say, liters of fuel the pump transfers per second) multiplied by the pressure (which pressure is at the exit of the pump). So, it's not the flow - it's the pressure where Raptor has a big advantage over F-1, and that pressure allows to have a better Isp.
And of course the better Isp allows to reach bigger characteristic velocity (or just a velocity in a free space, where gravity or atmosphere don't get in the way) using the same amount of fuel.
The logic goes roughly like that. Every rocket engine designer wants to reach bigger Isp. For that, using a particular fuel, one need to reach bigger pressure in the chamber, and we move from pressure-fed engines (like the first French orbital rocket, Diamant, which had pressure-fed first stage) to pumps, because high-pressure tanks are too heavy. Pumps initially are open cycle, or gas generator cycle, but we throw away enough gases after the pumps' turbine, so next improvement is we get a closed cycle. With closed cycle we can choose to use all fuel or all oxidizer to move the turbine, but as soon as some component is used fully, we can't get more energy for pumps. Eventually we go to the more complex full-flow cycle, which uses both components and reaches the highest pressure in the chamber.
The next step would probably be a detonation engine :) which uses somewhat more efficient process to convert chemical energy into speed, but it's not yet developed enough. We can also talk about more heat-resistant turbines which would allow to extract more energy from the fuel and to increase pressure some more... but there we also have a lot of R&D ahead of us.
Correct for Raptor 2. Raptor 3 is closer to half [1][2].
Not sure why people are downvoting you, but objectively the Raptor really is a marvel of engineering itself (maybe less than the F-1 that was created with slide rules at the time, but it does seem poised to upend space flight again).
Power = Force * Velocity = Thrust * exhaust velocity = Thrust * Specific Impulse * 9.80665
Did we invent kerolox as a portmanteau in the last 10 years? This article is a total time warp.
Designs for this magnificent beast were probably started shortly into the Sputnik scare. At the time, the Soviet space program technical capabilities were overestimated by almost everyone because the Soviets managed to hit a bunch of milestones first by, essentially, being OK with taking on more risk.
Correction: Soviet (liquid fuel) rocket engines became world state of the art in 1950-s and mostly remained as such till about 2010. Rocket engines is the technology which is enabler to most - relatively simple, looking from today - space flights of 20th century.
One can't hit a bunch of milestones first just by chance - you have to have something behind it, and in addition to engines there were a lot of less-than-announced flights - remember how the back side of the Moon was successfully photographed only on the third flight and soft landing on the Moon took quite a few more attempts?
One can't be about as successful as the other guy in terms of deaths in space just because of luck - corner cutters were on the both sides of the Iron Curtain, but there were also understanding that you'll lose all your advantage by just having a few more deaths. No amount of successes in unmanned flights will help (because people are much more interested in manned flights), so you just can't really allow people to die - in USSR you could also have very personal displeasures of uncomfortable size.
In "History of Liquid Propellant Rocket Engines" George Sutton mentions that USSR made about 10 times more liquid fuel rocket engine designs than USA. That should bring some perspective to the matters.
It's absolutely bizarre to me to watch ancient Disney videos featuring Wernher von Braun discussing guided missiles and doing his best to downplay his German accent.
If this doesn't spell defeat, I don't know what does. The richest country in the world is too poor for space launches. Or too cheap.
> There has never been anything like the Saturn V, the
> launch vehicle that powered the United States past the Soviet
> Union to a series of manned lunar landings in the late
> 1960s and early 1970s. The rocket redefined "massive,"
> standing 363 feet (110 meters) in height and producing a
> ludicrous 7.68 million pounds (34 meganewtons) of thrust
> from the five monstrous, kerosene-gulping Rocketdyne
> F-1 rocket engines that made up its first stage.
I do think it was an interesting option to replace the SRBs on SLS but alas we'll never know.
@dang, can we add the year to the headline? Thank you.